Composite explosive signal transmission cord and method of making same



INVENTORS DAVID J. ANDREW ALVIN E. TANNER ATTORNEYS D. J. ANDREW E L COMPOSITE EXPLOSIVE SIGNAL TRANSMISSION CORD AND METHOD OF MAKING SAME Filed May 6, 1963 I I I I I I I I I I March 22, 1966 United States Patent Ofiice 3,241,489 Patented Mar. 22, 1966 3,241,489 COMPOSITE EXPLOSIVE SIGNAL TRANSMISSION CURD AND METHOD OF MAKING SAME David J. Andrew and Alvin E. Tanner, Simsbury, Conn, assignors to Ensign-Eickford Company, Simsbury,

Conan, a corporation of Connecticut Filed May 6, 1963, Ser. No. 278,299 9 Claims. (Cl. 102-27) The present invention generally relates to a signal transmission cord and more particularly to an improved explosive-filled composite detonating and connecting cord suitable for directly initiating explosive charges and a novel method of making such a cord.

It is an object of the present invention to provide a composite explosive signal transmission cord which is both self-propagating for transferring a low energy signal and capable of performing useful, comparatively high energy work at one or more work stations along its length.

Another object of the present invention is to provide a unitary, composite cord of high reliability which both conveys an explosive signal between selected locations while performing explosive work at one or more pre-selected locations along the length of the cord.

A further object of the present invention is to provide an improved method for producing a composite, unitary cord having low cost yet possessing a high degree of reliability.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application which will be indicated in the appended claims.

In the drawings:

FIG. 1 is a plan view, partially in section anclpartially broken away, of one embodiment of the present invention;

FIG. 2 is a fragmentary plan view of another embodiment of the present invention;

FIG. 3 is a fragmentary view of a complete assembly of the embodiment of FIG. 2, the enclosing structure being shown in longitudinal cross section;

FIG. 4 is a fragmentary plan view of still another embodiment of the present invention;

FIG. 5 is a fragmentary plan view of a further embodiment of the present invention;

FIG. 6 is a fragmentary plan view, partially in section, of a further embodiment of the invention; and

FIG. 7 is a transverse cross-sectional view taken along the line 77 of 'FIG. 6.

Referring now to the drawings in greater detail, FIG. 1 shows a preferred embodiment of the composite cord 10 of the present invention used in explosive signal transmission and utilization systems. Such systems have been proposed in recent years with increasing frequency as substitutes for mechanical, electrical, and hydro-pneumatic control systems for such applications as initiating a main explosive charge in releasing canopies on damaged airplanes and ejecting a pilot from such a craft. Such substitution is occurring more frequently because electrical systems are subject to accidental initiation by spurious electrical signals and malfunction due to switch and power source failures, whereas hydraulic or pneumatic systems require bulky and heavy pressure controlling apparatus and are subject to the safety hazard of escaping noxious gases.

The explosive connecting cord of US. Patent No. 2,982,210, assigned to the assignee of the present invention, very successfully provides the control signal transmission function of the control system mentioned heretofore by rapidly and reliably self-propagating the explosive signal over the length of the cord with a maximum of safety. However, such a cord is characterized by low energy availability for the ultimate load or control device thereby requiring the addition of energy boosters or amplifiers to raise the available energy level to a point sufficient to initiate the load device. Each such booster seriously detracts from the reliability of the system because it provides an explosive interface over which the signal must be transmitted. Efforts to increase reliability of the system using accessory type boosters have required comparatively large quantities of more sensitive explosives thereby increasing the cost of the system and even such efforts have not achieved the necessary reliability.

In accordance with the present invention, it has been found that it is possible to substantially eliminate these disadvantages and reduce the number of possible failure modes in an explosive system by utilizing a composite cord 10- of a unitary construction having a connecting portion 12 and a detonating or booster portion 14. Composite cord 10 consists of a continuous homogeneous core 16 containing the explosive charge and a continuous sheath 18 encasing the core throughout its entire length.

Connecting portion 12 is of generally low brisance and is capable of reliably transmitting an explosive signal from one place to another without creating an environmental hazard. It is similar in construction to the connecting cord disclosed in the aforementioned United States Patent No. 2,982,210 and contains a suitable explosive load in core 16. It is generally desired that portion 12 be incapable of lateral transmission of a detonating stimulus and may contain a core load typical of low energy or mild detonating cords, i.e., core loads of at least 0.1 grain per linear foot. Connecting portion 12 is relatively flexible and ,may be provided with a suitable covering, shown in FIG. 3 and generally designated 30, to provide protection from abrasive wear or other environmental conditions while at the same time confining the lateral explosive effect.

Detonating or booster portion 14 of unitary composite cord 10 is of greater diameter than connecting portion 12 and has a core 16 that is continuous and homogeneous with core 16 of portion 12, as is sheath 18. The explosive load in core 16 of booster portion 14 is of greater quantity than that found in connecting portion [12 and is sufiicient to increase the intensity of the explosion to a point where useful explosive work or detonating stimulus will be produced. The booster core load may be as high as 150 grains per linear foot or higher, but is generally from about 10 to grains per linear foot, for example 25 to 40 grains per linear foot and preferably about -30 grains per linear foot. That concentration of explosive results in a useful work station which is characterized by high brisance and the ability to transmit the explosive signal while providing a detonating stimulus. The length of bell-shaped booster 14 shown in FIG. 1 can, of course, vary depending upon the results to be achieved.

The use of a unitary construction containing a booster station possesses the advantage of eliminating the failure mode occasioned by transmitting the explosive signal across an explosive interface provided by an accessory booster, while at the same time reducing the explosive charge required by a conventional auxiliary booster. More specifically, to produce the effect obtained with the present invention by means of conventional explosive cords requires that a low brisance connecting cord be cut or sliced open and increased quantities of explosive (often a more sensitive explosive) be added at the cut to produce an accessory booster possessing sufiicient brisance to be capable of performing the desired useful work functions. This method results in an explosive interface which appreciably reduces the reliability as well as the safety of the cord while increasing the cost. Consequently, more important than the economic saving in labor and the amount of explosive necessary is the added reliability and safety of the present invention.

The explosive utilized in the core is a generally crystalline cap-sensitive high explosive. Those which have been found suitable for use in accordance with the present invention include: pentaerythritetranitrate (PETN), cyclotriimethylenetrinitramine (RDX), cyclotetramethylenetrinitramine (HMX) and TACOT-TN (a dibenzo- 1,2,5, 6-tetraazacyclooctatetraene made by E. I. du pont de Nemours & Company).

Sheath 18 for core 16 should be of such material as will provide the necessary physical strength, mechanical shape and protection for the explosive from the environment. It is preferred to use a sheath of metal such as lead or aluminum; however, nonmetallic material may be substituted. If desired a covering 30 may be placed on the sheath comprising material such as a woven fabric, extruded synthetic compositions and natural flexible materials, rubber fi'ber glass or such other covering as is desired. The exact parameters of the explosive core, the sheath and the reinforcing structure may vary in accordance with the conditions to which the article is subjected during its use.

Referring now to FIGS. 24 wherein the same numerals refer to similar parts, there is shown two modifications of a booster station 14 located at a terminal point in the cord. In FIGS. 2 and 3 booster 14 contains a transverse slot 20 having an angle alpha (a) shown as being about 90 degrees. Such a structure is readily adapted to the initiation of a suitably shaped linear charge by applying transverse slot 20 to the top side of such a charge. FIG. 4 shows booster 14 containing conical groove 22 in the core 16 of the cord. Conical groove 22 has an angle beta (,6) which is shown to be about 60 degrees and is located centrally in FIG. 4 although it may effectively be located at some point other than the center of core 16. These configurations may be utilized to enhance the initiation of other explosive charges over a gap or may be used separately for puncture of a hole. 'Further, where conical groove 22 is located other than centrally in the core, it might serve usefully in a hookup where it is desired to have the provision of looping so the detonation could proceed in either direction. Additionally, it might provide a suitable orientation technique with another offcenter groove, thus enhancing the reliability across the gap. The terminal bell-shaped booster 14 could also be used to initiate a series of transmission lines to carry signals to a multiplicity of points; e.g., eight lines could be afiixed to the flat faced surface 24 of core 16 in FIG. 1.

FIG. 5 shows another embodiment of the composite cord wherein the detonating station 14 is located intermediate the low brisance end portions 12. Such an arrangement provides a detonating stimulus at an intermediate work point along the signal transmission system thereby permitting innumerable adaptations of the present invention utilizing the lateral detonating capabilities of the composite cord.

FIGS. 6 and 7 show a modification of a centrally or intermediately located booster station. Booster 14 is shown as having a linear configuration containing V- shaped cavity 26 which provides a typical cutting action along the length of the charge. Further combinations and modifications of these various embodiments will be apparent to those skilled in the art.

The composite cord of the present invention is made by initially forming a detonating fuse of uniform diameter throughout its length and subsequently reducing the diameter of the fuse in those areas of the tube where only signal transmission of low brisance is desired. The initially formed fuse may be constructed by filling a metal tube, such as a lead tube, with the desired explosive powder in a quantity determined by the inside diameter of the tube, density of packing, etc., and then forming such as by drawing the filled tube through a series of dies or rolls, thereby obtaining the desired uniform diameter. During this operation or subsequent thereto, cavity 26 may be formed in cord 10 in the normal manner.

The diameter of the uniform fuse is then reduced by working or forming along its length except in those areas where work stations are to be located. The working produces an outside diameter in the connecting portion which may be about one-half and preferably one-fifth or less, for example one-twentieth, the diameter of the work station. It has been found that the working or forming operation producing the highest degree of uniformity and reliability is a swaging operation although rolling will also produce good results. The swaging or rolling of the filled tube not only causes it to elongate but also densifies the explosive in the areas of reduced diameter.

In order to more fully understand the present invention, the following specific example is given by way of illustration without in any way limiting the invention thereby.

Example A lead tube having an inside diameter of 0.250" and an outside diameter of 0.375" is filled with enough pentaerythritol tetranitrate (PETN) explosive so that when the tube is drawn to an outside diameter of 0.212 the resulting explosive core load will be 28 grains per linear foot. The explosive-filled tube is then drawn to the uniform outside diameter of 0.212. The diameter of the tube is subsequently further reduced by swaging, from the previous uniform 0.212" to an outside diameter of 0.04. The swaging operation is performed on the entire length of the tube with the exception of about 0.250" at one end thereof, which portion will constitute the work station. The swaging results in a core load, at the reduced diameter, of 1 grain per linear foot. The portion having a diameter of 0.04" is alternately covered, as shown in FIG. 3, with a vinyl tube 32, a braided jacket 34 consisting of three layers of rayon and two layers of fiberglass and a final vinyl plastic jacket 36. The end of the 0.250" long portion remaining at the initially drawn diameter of 0.212" is covered with a thin film, 0.002", of a potting compound 38; a piece of aluminum foil 40 is placed over the end face of the cord and finally an outer sleeve 42 is placed over the potting compound 38 as well as a portion of the adjacent braided jacket. The braided jacket and booster endv are thus potted in the sleeve.

As can be seen from the foregoing description, the present invention provides a signal transmission cord which is modified so as to provide useful work at lateral and terminal work output stations. The cord, which comprises a continuous explosive core load contained within a continuous sheath, is capable of conveying its own initiation signal from an initiation point through one or more intermediate work output stations to an end termination point or work station without providing detrimental explosive interfaces or excessive explosive side effects, such as fragmentation, noxious gases, etc. The present invention additionally provides a structure which is simple in design, requires less explosive charge at the booster portion and is extremely reliable to use. Further, the present invention provides a composite cord of unitary construction capable of initiating numerous explosive charges while at the same time carrying the detonating signal from one place to another.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above described will become readily apparent without departure from the spirit and scope of the invention, the scope of which is defined in the appended claims.

We claim:

1. A high explosive, composite cord of unitary construction having a connecting portion of generally low brisance, at least one detonating portion of sufficient brisance to provide useful explosive work integral with said connecting portion, a core containing a high velocity detonating explosive extending continuously through said connecting portion and said detonating portion, the explosive in said core having a detonation velocity substantially greater than 2 ft./se-c. and a continuous sheath encasing the core and said portions throughout the length thereof.

2. A high explosive, composite cord of unitary construction having a connecting portion of generally low :brisance, at least one booster of sufiicient brisance to provide useful explosive work, a core of high velocity detonating explosive extending continuously through each booster and each portion of generally loW brisance, the explosive in said core having a detonating velocity substantially greater than 2 ft./sec. and a continuous sheath encas-ing the core throughout its length, said core having a substantially greater amount of explosive per unit length at each booster than at each connecting portion.

3. A cord as set forth in claim 1 wherein one detonating portion is located atone end of the cord.

4. A cord as set forth in claim 3 wherein the explosive core in the detonating portion is generally bell shaped.

5. A cord as set forth in claim 1 wherein one detonating portion is located intermediate the ends of the cord.

6. A cord as set forth in claim 1 wherein the core comprises at least 0.1 to 4 grains per linear foot of detonating explosive along its entire length.

7. A cord as set forth in claim 2 wherein the core of each booster comprises from 10 to grains per linear foot of detonating explosive.

8. A cord. as set forth in claim 2 wherein the outside diameter of each booster is about five times that of the connecting portion.

9. A cord as set forth in claim 8 wherein at least one booster is a linear shaped charge.

References Cited by the Examiner UNITED STATES PATENTS 1,155,230 9/1915 Graham 102-27 1,275,001 8/1918 Dormer 102-27 1,923,761 8/1933 Snelling et al. 86-1 2,543,057 2/ 1951 Porter.

2,558,134 6/1951 Hall 102,27 2,675,882 4/1954 BaZZoni et al. 10222 X 2,863,353 12/1958 Brirnley 861 2,982,210 5/1961 Andrew et a1. 10227 BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL FEINBERG, Examiner. 

1. A HIGH EXPLOSIVE, COMPOSITE CORD OF UNITARY CONSTRUCTION HAVING A CONNECTING PORTION OF GENERALLY LOW BRISANCE, AT LEAST ONE DETONATING PORTION OF SUFFICIENT BRISANCE TO PROVIDE USEFUL EXPLOSIVE WORK INTERAL WITH SAID CONNECTING PORTION, A CORE CONTAINING A HIGH VELOCITY DETONATING EXPLOSIVE EXTENDING CONTINUOUSLY THROUGH SAID CONNECTING PORTION AND SAID DETONATING PORTION, THE EXPLOSIVE IN SAID CORE HAVING A DETONATION VELOCITY SUBSTANTIALLY GREATER THAN 2 FT./SEC. AND A CONTINUOUS SHEATH ENCASING THE CORE AND SAID PORTIONS THROUGHOUT THE LENGTH THEREOF. 